Finder optical system and image pickup apparatus including the same

ABSTRACT

A finder optical system includes an erecting optical system, an eyepiece optical system, and a light metering optical system. An optical axis of the light metering optical system is non-parallel to an optical axis of the eyepiece optical system. The light metering optical system includes a first lens having positive refractive power and a second lens having negative refractive power in this order from a side of the erecting optical system to a side of an image sensor, and the second lens is a prism body reflecting a light flux incoming from an incident surface off an inner reflection surface and outputting the light flux from a light outputting surface.

BACKGROUND

1. Field of Art

The present disclosure relates to a finder optical system and an imagepickup apparatus including the same. The present disclosure specificallyrelates to a finder optical system and a light metering optical systemwhich are suitable for an image pickup apparatus such as a single-lensreflex camera. The finder optical system includes an eyepiece opticalsystem and a light metering optical system. The eyepiece optical systemallows an observer to observe an object image formed on a focusingscreen. The light metering optical system is configured to re-image theobject image formed on the focusing screen on an image sensor to providean electronic image.

2. Description of the Related Art

In a finder optical system in Japanese Patent Application Laid-Open No.2007-93888, an electronic image is obtained by re-imaging an objectimage formed on a focusing screen on an image sensor in a light meteringoptical system via an erecting optical system. The finder optical systemhas a function of recognizing a face of an object and adjusting focusand exposure, a function of moving a focusing point along with movementof the object, and a function of displaying the object image in realtime on a liquid crystal screen provided on a back surface of a camerabody. The finder optical system in Japanese Patent Application Laid-OpenNo. 2007-93888 also includes on a light exit side of a pentagonal prisma light path dividing unit. The light path dividing unit is a halfmirror for dividing a light path into a path for guiding light to theimage sensor via the light metering optical system and a path forguiding light to an eyepiece optical system.

Also is known a camera light metering apparatus in which light receivinglenses constituting an eyepiece optical system and a light meteringoptical system are arranged side by side on a side of a light exitsurface of a pentagonal roof prism. In Japanese Patent ApplicationLaid-Open No. 63-74042, a light metering lens including an innerreflection surface is used as the light metering optical system to guidea light flux exiting from the pentagonal roof prism to a light receivingelement.

To pick up a bright and high-quality electronic image at the time ofpicking up an image by forming an object image on the image sensor withuse of the light metering optical system, a bright light meteringoptical system and a high-pixel-number and large-sized image sensor arerequired.

On the other hand, to observe the object image formed on a focusingscreen in a bright state, a large-diameter lens needs to be used for theeyepiece optical system.

To pick up a high-quality image in real time and observe a bright objectimage via the eyepiece optical system, the light metering optical systemincluding the large-sized image sensor and the large-diameter eyepieceoptical system must be arranged side by side on the light exit side ofan erecting optical system. However, the image sensor and the eyepieceoptical system mechanically interfere with each other, which makes itdifficult to dispose both of them.

As shown in the light metering apparatus in Japanese Patent ApplicationLaid-Open No. 63-74042, by inclining an optical axis of the lightmetering optical system toward an optical axis of the eyepiece opticalsystem, mutual interference can be avoided easily. However, when theobject image formed on the focusing screen is re-imaged on the imagesensor in a state in which the optical axis of the light meteringoptical system is inclined toward a normal line of the focusing screen,asymmetric curvature of field and astigmatism occur depending on animage height, which makes it difficult to pick up a high-quality image.

SUMMARY

According to an aspect of the present disclosure, a finder opticalsystem includes an erecting optical system causing an object imageformed on a focusing screen by an imaging optical system, to be an erectimage, an eyepiece optical system forming the object image caused to bethe erect image by the erecting optical system, and a light meteringoptical system forming the object image focused on the focusing screen,on an image sensor via the erecting optical system. An optical axis ofthe light metering optical system is non-parallel to an optical axis ofthe eyepiece optical system, the light metering optical system includesa first lens having positive refractive power and a second lens havingnegative refractive power in this order from a side of the erectingoptical system to a side of the image sensor, and the second lens is aprism body reflecting a light flux from an incident surface off an innerreflection surface and outputting the light flux from a light outputtingsurface.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 is a schematic configuration diagram of an image pickup apparatusincluding a finder optical system according to an exemplary embodimentof the present invention.

FIG. 2 is a developed view along an optical axis of a light meteringoptical system of a finder optical system according to a first exemplaryembodiment of the present invention.

FIG. 3 is a developed view along an optical axis of a light meteringoptical system of a finder optical system according to a secondexemplary embodiment of the present invention.

FIG. 4 is a developed view along an optical axis of a light meteringoptical system of a finder optical system according to a third exemplaryembodiment of the present invention.

FIG. 5 is an enlarged view around a surface of a second lens on a sideof an image sensor in the light metering optical system of the finderoptical system according to the third exemplary embodiment of thepresent invention.

FIG. 6 is a developed view along an optical axis in the light meteringoptical system of a finder optical system according to a fourthexemplary embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

A finder optical system according to an exemplary embodiment of thepresent invention includes an erecting optical system such as apentagonal roof prism causing an object image formed on a focusingscreen by an imaging optical system (objective lens) to be an erectimage. The finder optical system also includes an eyepiece opticalsystem enlarging and forming as a virtual image the object image whichis the erect image made by the erecting optical system. The finderoptical system further includes a light metering optical system forshrinking and imaging the object image formed on the focusing screen, onan image sensor via the erecting optical system. An optical axis of thelight metering optical system passes through a center of the focusingscreen and is inclined (non-parallel) toward an optical axis of theeyepiece optical system.

An image picked up by the image sensor is utilized for recognition anddisplay of the object image and is utilized for measurement (lightmetering) of brightness of an object. The light metering optical systemand the eyepiece optical system are arranged so that respective surfacesthereof on a side of light entrance is opposed to a surface of theerecting optical system on a side of light exit. In addition, the lightmetering optical system is arranged on an opposite side of the imagingoptical system with respect to the optical axis of the eyepiece opticalsystem.

The light metering optical system includes an aperture stop, a firstlens having positive refractive power, and a second lens having negativerefractive power in this order from a side of the erecting opticalsystem to a side of the image sensor. The second lens is a prism bodyspecularly or totally reflecting a light flux incoming from a lightentrance surface on an inner reflection surface and outputting the lightflux from a light outputting surface.

FIG. 1 is a schematic view of a main part of an image pickup apparatus(a single-lens reflex camera) including a finder optical system 101according to an exemplary embodiment of the present invention. FIG. 2 isa developed view along an optical axis in a light metering opticalsystem of a finder optical system according to a first exemplaryembodiment of the present invention.

In the image pickup apparatus in FIG. 1, when an object image isobserved through the finder optical system, light passing through animaging optical system (objective lens) 11 is reflected on a quickreturn mirror 12, and the object image is formed on a focusing screen13.

The object image formed on the focusing screen 13 by the imaging opticalsystem 11 becomes erected by a pentagonal roof prism 15. The erect imageis observed by an observer through an eyepiece optical system 16. Thefinder optical system also includes a light metering optical system 2having an optical axis Ob passing through a center of the focusingscreen 13 and inclining toward an optical axis Oa of the eyepieceoptical system 16.

The light metering optical system 2 of the finder optical systemaccording to the first exemplary embodiment is arranged on an upper sideof the eyepiece optical system 16. The upper side of the eyepieceoptical system 16 means an opposite direction of the imaging opticalsystem 11 with respect to the optical axis Oa of the eyepiece opticalsystem 16. The light metering optical system 2 includes an aperture stopST, a dust-proof filter 23, a first lens 17 having positive refractivepower, and a second lens 18 having negative refractive power in thisorder from a side of the pentagonal roof prism 15 to a side of an imagesensor 20. The second lens 18 is provided with a reflection surface(rear reflection surface) 18 a utilizing specular reflection or totalreflection, and a light path of the light metering optical system 2 isbent upward. The finder optical system includes a filter 19 such as alow-pass filter and an IR (near-infrared) cut filter and the imagesensor 20 such as a charge-coupled device (CCD).

By arranging a lens surface 18 b of the second lens 18 on a side of theimage sensor 20 and the image sensor 20 above the eyepiece opticalsystem 16, mechanical interference between the light metering opticalsystem 2 and the eyepiece optical system 16 can be avoided.Alternatively, by bending the light path of the light metering opticalsystem 2 in a direction vertical to the drawing sheet in FIG. 1,mechanical interference between the light metering optical system 2 andthe eyepiece optical system 16 can also be avoided.

The object image formed on the image sensor 20 by the light meteringoptical system 2 is subjected to image processing at an image processingunit 21 and is displayed in real time on a liquid crystal screenprovided on a back surface of a camera body. The object image is alsoused for focusing along with movement of a main object in the image.

An image sensor 22 is a charge coupled device (CCD) or a complementarymetal-oxide semiconductor (CMOS) recording (light-receiving) the objectimage formed by the imaging optical system 11 when the quick returnmirror 12 is turned upward.

FIG. 2 is a developed view of the light metering optical system 2, andthe filter 19 and the image sensor 20 arranged close to the lightmetering optical system 2 in the finder optical system according to thefirst exemplary embodiment when the light metering optical system 2, thefilter 19, and the image sensor 20 are developed along the optical axisOb. The light metering optical system 2 includes the aperture stop ST,the dust-proof filter 23, the first lens 17, and the second lens 18 inthis order from an object side (a side of the pentagonal roof prism 15).In a case where image forming is performed only by the first lens 17,image forming performance is relatively favorable around the opticalaxis Ob. However, since a Petzval sum is large, curvature of field andastigmatism cannot be corrected at an area away from the optical axisOb, and image forming performance on the periphery cannot be secured.Under such circumstances, by introducing the second lens 18 havingnegative refractive power and decreasing the Petzval sum, curvature offield and astigmatism can be corrected to secure image formingperformance on the periphery.

More desirably, the surface 18 b of the second lens 18 on the side ofthe image sensor 20 has negative refractive power and is in an asphericshape in which an absolute value of the refractive power increases froma center to a periphery. The curvature of field is aberration in whichan image forming position in an axial direction of light is displaceddepending on an image height and is corrected most effectively when itis corrected at the lens surface 18b, which is closest to the imagesensor 20. When correction of the Petzval sum is insufficient, an imageplane is curved in a direction of the second lens 18 from a center to aperiphery. Accordingly, the surface 18 b of the second lens 18 on theside of the image sensor 20 is formed in the aspheric shape in which theabsolute value of the refractive power increases from the center to theperiphery, so that the image forming position of a peripheral light fluxshifts to the image sensor 20 side and the curvature of field can becorrected favorably.

A focal length of the entire lens of the light metering optical system 2is f while a focal length of the second lens 18 is f2. At this time, thefollowing condition is desirably satisfied.

f2/f<−1.9   (1)

Condition (1) relates to a ratio between the focal length of the secondlens 18 and the focal length of the entire lens of the light meteringoptical system 2. By satisfying Condition (1), various kinds ofaberration such as the curvature of field can be reduced easily. Anupper limit of Condition (1) should not be exceeded since this makes itdifficult to correct various kinds of aberration such as the curvatureof field, which lowers an image quality around the screen.

FIG. 3 is a developed view of the light metering optical system 2, andthe filter 19 and the image sensor 20 arranged close to the lightmetering optical system 2 in a finder optical system according to asecond exemplary embodiment when the light metering optical system 2,the filter 19, and the image sensor 20 are developed along the opticalaxis Ob. The second exemplary embodiment has a basic configuration incommon with the first exemplary embodiment and differs from the firstexemplary embodiment only in terms of shapes of the first lens 17 andthe second lens 18.

The light metering optical system 2 in a finder optical system accordingto a third exemplary embodiment will be described with reference toFIGS. 4 and 5. FIG. 4 is a developed view of the light metering opticalsystem 2, and the filter 19 and the image sensor 20 arranged close tothe light metering optical system 2 in the finder optical systemaccording to the third exemplary embodiment when the light meteringoptical system 2, the filter 19, and the image sensor 20 are developedalong the optical axis Ob. FIG. 5 is an enlarged view around the surface18 b of the second lens 18.

FIG. 5 has a tangent line (a tangent plane) 18 bb to a top 18 b 1 as anintersection point of the lens surface 18 b with the optical axis Ob (anoptical axis 17 a of the first lens 17) of the light metering opticalsystem 2. FIG. 5 also has a perpendicular line Obb to the optical axisOb of the light metering optical system 2. FIG. 5 further has a normalline (a surface normal) 18 b 2 passing the top 18 b 1. A center ofcurvature 18 b 3 of the lens surface 18 b is located off the opticalaxis Ob of the light metering optical system 2. The optical axis Ob ofthe light metering optical system 2 is inclined (non-parallel) towardthe optical axis Oa of the eyepiece optical system 16.

In the present exemplary embodiment, the optical axis Ob of the lightmetering optical system 2 is parallel to a normal line 20 a of an imagepickup surface of the image sensor 20. Since the light metering opticalsystem 2 picks up the object image on the focusing screen 13 in anoblique direction, an upper side and a lower side of the image sensor 20have different image forming characteristics. In the present exemplaryembodiment, to eliminate this difference in image formingcharacteristics, the surface 18 b closest to the image sensor 20 isinclined toward the normal line 20 a of the image sensor 20. In thepresent exemplary embodiment, the normal line 18 b 2 passing the top 18b 1 of the lens surface 18 b is inclined at an angle of 2.5° toward theoptical axis Ob of the light metering optical system 2 in a direction ofthe optical axis Oa of the eyepiece optical system 16. That is, thenormal line 18 b 2 passing the top 18 b 1 of the lens surface 18 b isinclined to be nearly parallel to the optical axis Oa of the eyepieceoptical system 16 compared with the optical axis Ob of the lightmetering optical system 2 is. Thus, the difference in image formingcharacteristics occurring between the upper side and the lower side ofthe image sensor 20 is reduced, and a favorable image can be picked upover the entire screen.

The light metering optical system 2 in a finder optical system accordingto a fourth exemplary embodiment will be described with reference toFIG. 6. In the present exemplary embodiment, the normal line 18 b 2passing the top 18 b 1 of the lens surface 18 b is inclined at an angleof 1.5° in a direction of the optical axis Oa of the eyepiece opticalsystem 16 toward the optical axis Ob of the light metering opticalsystem 2. That is, the normal line 18 b 2 passing the top 18 b 1 of thelens surface 18 b is inclined to be nearly parallel to the optical axisOa of the eyepiece optical system 16 compared with the optical axis Obof the light metering optical system 2.

Also, the normal line 20 a of the image sensor 20 is inclined (i.e.,non-parallel) at an angle of 1.0° in a direction away from the opticalaxis Oa of the eyepiece optical system 16 toward the optical axis Ob ofthe light metering optical system 2. That is, the normal line 20 a ofthe image sensor 20 is inclined to become less parallel to the opticalaxis Oa of the eyepiece optical system 16 than to the optical axis Ob ofthe light metering optical system 2. Thus, the difference in imageforming characteristics occurring between the upper side and the lowerside of the image sensor 20 is reduced, and a favorable image can bepicked up over the entire screen.

Next, numerical examples of the light metering optical systems in thefinder optical systems of each exemplary embodiment will be described.In the numerical examples, “i” represents an order of a surface wherethe aperture stop ST is a first surface (r1). “ri” represents a paraxialcurvature radius of an i-th surface including the aperture stop ST. “do”represents a distance between the aperture stop ST and a designed dummysurface (r2). “di” represents an axial surface distance between an(i+1)-th surface from the aperture stop ST and an (i+2)-th surface.Further, “Ni” represents a refractive index of an i-th material from theaperture stop ST in terms of a d line (wavelength=578.56 nm), and “vi”represents an Abbe number of an i-th material from the aperture stop STin terms of the d line. Further, “f” is a focal length, and “FNO.” is anF-number.

“r1” represents the aperture stop ST, “r2” represents the designed dummysurface, and “r3” and “r4” represent each surface of the dust-prooffilter 23. “r5” and “r6” represent each surface of the first lens 17,and “r7” and “r8” represent each surface of the second lens 18. “r9” and“r10” represent each surface of the filter 19. “r11” corresponds to theimage sensor 20. The aspheric surface shape is defined by the followingequation.

$x = {\frac{\frac{h^{2}}{R}}{1 + \sqrt{1 - \left( \frac{h}{R} \right)^{2}}} + {\sum\limits_{j}{C_{j}h^{j}}}}$

In the equation representing the aspheric surface shape, “x” is adistance from a top of a lens surface in an axial direction of light,“h” is a height in a direction vertical to an optical axis, and “R” is aparaxial curvature radius at a top of a lens surface. “C_(j)” is anaspheric coefficient. “E-i” represents an exponential expression wherethe base is 10, that is, “10⁻¹.”

NUMERICAL EXAMPLE 1

f = 7.055 FNO. = 1.50 Curvature Axial surface Refractive Abbe radius[mm]distance[mm] index(Nd) number(νd) r1 = ∞ d0 = 2 r2 = ∞ d1 = 0.1 r3 = ∞d2 = 0.300 N1= 1.523 ν1 = 58.6 r4 = ∞ d3 = 0.100 r5 = 7.741153 d4 = 1.86N2 = 1.58913 ν2 = 61.28 r6 = −7.13296 d5 = 0.427 r7 = 192.91412 d6 =6.00 N3 = 1.58306 ν3 = 30.23 r8 = 23.89 d7 = 2.00 r9 = ∞ d8 = 0.5 N4 =1.52 ν4 = 55.0 r10 = ∞ d9 = 0.4 r11 = ∞ [Aspheric coefficient] Surfacenumber r5 C4 = 7.479583E−005 C6 = −1.271707E−003 C8 = 1.189772E−004 C10= −3.296993E−006 C12 = 0 r7 C4 = −3.283715E−003 C6 = 3.293603E−003 C8 =−5.410181E−004 C10 = 3.855315E−005 C12 = −7.644431E−007 r8 C4 =6.903753E−003 C6 = −3.719096E−003 C8 = 8.556452E−003 C10 =−1.089785E−002 C12 = 6.938947E−003 C14 = −1.939813E−003 C16 =1.954886E−004 f2/f = −27.3

NUMERICAL EXAMPLE 2

f = 7.055 FNO. = 1.50 Curvature Axial surface Refractive Abbe radius[mm]distance[mm] index(Nd) number(νd) r1 = ∞ d0 = 2 r2 = ∞ d1 = 0.1 r3 = ∞d2 = 0.300 N1 = 1.523 ν1 = 58.6 r4 = ∞ d3 = 0.100 r5 = 5.52630 d4 = 1.86N2 = 1.58913 ν2 = 61.28 r6 = −12.89385 d5 = 0.40 r7 = ∞ d6 = 6.00 N3 =1.58306 ν3 = 30.23 r8 = 32.60351 d7 = 2.00 r9 = ∞ d8 = 0.5 N4 = 1.52 ν4= 55.0 r10 = ∞ d9 = 0.4 r11 = ∞ [Aspheric coefficient] Surface number r5C4 = −8.236507E−004 C6 = −4.410039E−004 C8 = 8.316892E−005 C10 =−8.480376E−006 C12 = 2.535400E−007 r7 C4 = 3.513226E−004 C6 =7.475901E−004 C8 = −1.886682E−004 C10 = 2.626060E−005 C12 =−1.324787E−006 r8 C4 = 1.836866E−002 C6 = −1.727160E−002 C8 =1.981183E−002 C10 = −1.602779E−002 C12 = 8.034174E−003 C14 =−2.134174E−003 C16 = 2.267634E−004 f2/f = −7.93

NUMERICAL EXAMPLE 3

f = 6.7 FNO. = 1.50 Curvature Axial surface Refractive Abbe radius[mm]distance[mm] index(Nd) number(νd) r1 = ∞ d0 = 2 r2 = ∞ d1 = 0.1 r3 = ∞d2 = 0.300 N1 = 1.523 ν1 = 58.6 r4 = ∞ d3 = 0.100 r5 = 5.3218 d4 = 2.500N2 = 1.851 ν2 = 40.1 r6 = −26.5344 d5 = 0.600 r7 = −12.155202 d6 = 5.500N3 = 1.585 ν3 = 29.0 r8 = 23.89 d7 = 1 r9 = ∞ d8 = 0.5 N4 = 1.52 ν4 =55.0 r10 = ∞ d9 = 0.4 r11 = ∞ [Aspheric coefficient] Surface number r5C4 = −6.3570E−004 C6 = 1.0903E−004 C8 = −2.3442E−005 C10 = 2.4558E−006C12 = −1.0866E−007 r8 C4 = −4.8762E−002 C6 = 1.2243E−001 C8 =−1.1818E−001 C10 = 6.4041E−002 C12 = −1.9210E−002 f2/f = −1.945

NUMERICAL EXAMPLE 4

f = 7.30 FNO. = 1.50 Curvature Axial surface Refractive Abbe radius[mm]distance[mm] index(Nd) number(νd) r1 = ∞ d0 = 2 r2 = ∞ d1 = 0.1 r3 = ∞d2 = 0.300 N1 = 1.523 ν1 = 58.6 r4 = ∞ d3 = 0.100 r5 = 5.52630 d4 =1.930 N2 = 1.58913 ν2 = 61.28 r6 = −12.8938 d5 = 0.427 r7 = ∞ d6 = 6.00N3 = 1.58306 ν3 = 30.23 r8 = 32.60351 d7 = 3.071 r9 = ∞ d8 = 0.5 N4 =1.52 ν4 = 55.0 r10 = ∞ d9 = 0.4 r11 = ∞ [Aspheric coefficient] Surfacenumber r5 C4 = 8.236507E−004 C6 = −4.410039E−004 C8 = 8.316892E−005 C10= −8.480376E−006 C12 = 2.535400E−007 r7 C4 = 3.513226E−004 C6 =7.475901E−004 C8 = −1.886682E−004 C10 = 2.626060E−005 C12 =−1.324787E−006 r8 C4 = 1.836866E−002 C6 = −1.727160E−002 C8 =1.981183E−002 C10 = −1.602779E−002 C12 = 8.034174E−003 C14 =−2.134174E−003 C16 = 2.267634E−004 f2/f = −1.8415

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-035913 filed Feb. 26, 2013, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A finder optical system comprising: an erectingoptical system configured to cause an object image formed on a focusingscreen by an imaging optical system to be an erect image; an eyepieceoptical system configured to form the object image caused to be theerect image by the erecting optical system; and a light metering opticalsystem configured to form the object image focused on the focusingscreen, on an image sensor via the erecting optical system, wherein anoptical axis of the light metering optical system is non-parallel to anoptical axis of the eyepiece optical system, the light metering opticalsystem includes a first lens having positive refractive power and asecond lens having negative refractive power in this order from a sideof the erecting optical system to a side of the image sensor, and thesecond lens is a prism body reflecting a light flux incoming from anincident surface off an inner reflection surface and outputting thelight flux from a light outputting surface.
 2. The finder optical systemaccording to claim 1, wherein the light outputting surface of the secondlens has negative refractive power and is in an aspheric shape in whichan absolute value of the refractive power changes increasing from acenter to a periphery.
 3. The finder optical system according to claim1, wherein, when a focal length of an entire lens of the light meteringoptical system is f while a focal length of the second lens is f2, acondition of f2/f<−1.9 is satisfied.
 4. The finder optical systemaccording to claim 1, wherein a line normal to a tangent plane at anintersection point of the light outputting surface of the second lenswith the optical axis of the light metering optical system and theoptical axis of the light metering optical system are non-parallel toeach other.
 5. The finder optical system according to claim 1, wherein anormal line of the image sensor and the optical axis of the lightmetering optical system are non-parallel to each other.
 6. An imagepickup apparatus comprising the finder optical system according toclaim
 1. 7. A light metering optical system configured to form an objectimage focused on a focusing screen, on an image sensor via an erectingoptical system, wherein an optical axis of the light metering opticalsystem is non-parallel to an optical axis of an eyepiece optical systemfor forming the object image via the erecting optical system, the lightmetering optical system includes a first lens having positive refractivepower and a second lens having negative refractive power in this orderfrom a side of the erecting optical system to a side of the imagesensor, and the second lens is a prism body reflecting a light fluxincoming from a light entrance surface off an inner reflection surfaceand outputting the light flux from a light outputting surface.
 8. Thefinder optical system according to claim 1, wherein a surface of a lensbetween the focusing screen and the image sensor has a center ofcurvature that is located off the optical axis of the light meteringoptical system.
 9. The finder optical system according to claim 1,wherein a normal line of a surface of a lens between the focusing screenand the image sensor is inclined toward with respect to a normal line ofthe image sensor such that it reduces distortions caused by imaging thefocusing screen at an angle.